1. Field
The present invention relates to a process for printing surfaces of wood-based flat elements (for example wooden panels), of any type and size and originating from any production process, even if already semi-finished (for example previously subjected to surface incision, surface smoothing, cutting, sawing, drilling, chamfering, surface treatment with chemical agents or water-based agents, coating agents, adhesive agents or sealing agents, or panels covered with sheets of paper or plastic, or already subjected to squaring or edging).
2. Description of Related Art
In particular, the wood-based flat elements in the present context are those made from a mass of wooden particles (commonly known as chipboard panels which, as is well known to the expert of the art, can be of standard type, of E2, E1 or E0 type, of so-called isocyanate type or of fire-retardant or waterproof type; or again of low density or medium density wood fibre type (commonly known as MDF: medium density fibreboard); or high density (commonly known as HDF: high density fibreboard); or so-called wet fibre panels, or oriented wooden strand panels, commonly known as OSB (oriented strands board). All these wood-based flat elements normally have a thickness varying between 0.5 mm and 50 mm, a width between 50 mm and 3400 mm, and a length between 100 mm and 5600 mm or more.
As is well known to the expert of this sector, the aforesaid wood-based panels are obtained from wood-based flat products produced using double-belt continuous presses, or by so-called multi-compartment or single-compartment presses (commonly known as Mende presses).
To obtain a wood-based panel presenting a printed surface, three different processes are currently used, namely:
1. In a first process, the relevant surface of the wood-based panels is clad with a paper sheet carrying the most varied motifs, for example a motif representing a wood type, a type of stone or rock, photographs, written texts, fantasy motifs, or simply a surface of a single colour.
The paper sheets are of so-called base printing paper, possibly of preimpregnated type, or of overlay paper. The printed sheets are obtained by preprinting operations, which as is well known to the expert of the art are fairly complex and require considerable time, and in particular:                graphic composition, i.e. the graphic design and development;        form construction, or incision (by various methods) of one or more printing cylinders;        cylinder installation on a rotogravure or flexographic printing machine and their adjustment.        
These preprinting operations together involve a downtime of the printing machine amounting to 6-8 hours, with the costs that this implies.
When printing has been carried out by said printing machine, the printed paper sheets obtained in this manner are applied to the wood-based panels. This is done by an impregnation operation (in which appropriate plants, known as impregnation plants, impregnate the printed sheets for example with thermosetting or vinyl adhesive agents, thermosetting urea or polyurethane resins). The impregnation operation is followed by a pressing operation by known hot pressing plants of various types, or by cold plants.
2. In a second known process the wood-based panels previously treated with sealants (such as fillers, lacquers or paper sheets) are printed directly. Also in this case preprinting operations are required, they being the same as for the first process, and as such are lengthy and costly. The wood-based panels are then directly printed.
3. The third known process is similar to the second, with the only difference that instead of a printing machine an ink-jet plotter is used, controlled by an electronic processor. As is well known, the panel to be printed is maintained at rest in the plotter, while the print heads (from one to four or more in number, one for each colour) move parallel to the surface to be printed. When the relative printing stage is complete, the panel advances through a distance equivalent to the width of the print head and the printing operation is repeated, and so on until the entire panel surface or that part thereof to be printed is complete.
As is well known to the expert of the sector, the printing process using a plotter is of low productivity (among the slowest of printing processes), and hence is unusable for large quantities. It also has a very high unit cost.
Again in this case preprinting operations are required, but comprise only graphic composition using suitable hardware supports and software obtainable commercially, plus a scanner.
In contrast to the first two, this third process using an ink-jet plotter enables surface which are not perfectly smooth to be printed.